Data transmission lines or buses are used to transfer data between the components of computers and other digital data systems. While the components of a computer, for example, generally handle data in a "single-ended" form, i e , a single conductor is either "high" or "low", differential swing transmission lines are typically used to transmit data between the CPU and other components of the computer. The reason is that single-ended lines are susceptible to common mode noise, while a differential swing, two-wire line is not. In a differential swing system, the data are represented by the voltage differential between two lines (e.g., +V and -V), and this differential remains the same when both lines are subjected to outside influences.
This requires that a transmitter be provided at the input to a transmission line to convert the data from single-ended to differential form, and that a receiver be provided at the output of the transmission line to convert the data from differential to single-ended form. The transmitter/receiver pair at the input and output of the line are referred to in combination as a transceiver.
The transmitter must receive the single-ended input data and convert it into differential pulses with minimal skew, i.e., the corresponding rise and fall on the transmission line pair must occur at the same time. The receiver must receive the differential input and generate symmetrical output pulses. Particular problems are encountered when the devices are formed in CMOS, since the characteristics of CMOS devices vary with temperature. Thus temperature changes can cause the data on the transmission line to be skewed, and this can affect the symmetry of the single-ended output of the receiver.